In the conveying of liquids and gases by pipelines, particularly when the liquids or gases are corrosive, it is known to provide lengths of metal pipe each lined with suitable plastics material, such as for example a polymer, to provide a corrosion resistance. To join adjacent lined pipe lengths, it is known to weld together the adjacent ends of the outer metal pipe lengths, and connect the inner plastics linings by an electrofusion technique.
Such an arrangement is illustrated and described in British Patent Publication No. 2979135 where a tubular electrofusion fitting is provided on a metal inner supporting ring, and is inserted into the adjacent ends of two lined pipe lengths, the electrofusion fitting having heating coils in or adjacent its outer surface one to each end of the fitting with electrical leads overlying the fitting to be taken through the gap between the adjacent outer metal pipe lengths and to a source of electrical power. After heating the coils to melt the interface between the fitting and the inner plastics lining of the pipe lengths, to create an electrofused joint, the electrical leads are cut back close to the outer metal pipe lengths, which are then welded together, with the inevitable incorporation of the electrical lead ends in the weld and which contaminates the weld.
Contamination of the weld between the adjacent ends of the outer metal pipe lengths can have serious consequences, particularly when the pipe line is to be laid in the sea, and it is not unknown for such welded joints to fail as a consequence of the contamination of the weld.
In addition to weld contamination, it is known for the electrofused joint between the fitting and the lining of the pipe to fail as a consequence of heating wire movement during the heating phase. Such joints are not easy to test before a pipeline is put into service and should it be that the electrofused joint is compromised and fails in use, serious consequences can arise, particularly if the pipeline is in a sub-sea application where repair or replacement costs would be excessive.